The invention provides granules based on pyrogenic titanium dioxide, a process for preparing the granules, and the use thereof.
It is known that pyrogenic titanium dioxide can be prepared from TiCl4 by high temperature or flame hydrolysis (Ullmanns Enzyklopxc3xa4die der Technischen Chemie, 4th edition, vol. 21, page 464 (1982)).
Pyrogenic titanium dioxide is characterized by extremely finely divided particles, a high surface area (BET), very high purity, spherically shaped particles and a lack of pores. As a result of these properties, pyrogenic titanium dioxide is increasingly being considered as a support for catalysts (Dr. Koth et al., Chem. Ing. Techn. 52, 628 (1980)). For this application, pyrogenic titanium dioxide is shaped in a mechanical manner using, for example, tabletting machines.
The object of the invention is to produce spray-dried granules of pyrogenic titanium dioxide which can be used as a catalyst support.
The invention provides granules based on pyrogenic titanium dioxide with the following physico-chemical characteristics:
Average particle diameter: 10 to 150 xcexcm
BET surface area: 25 to 100 m2/g
pH: 3 to 6
Compacted density: 400 to 1,200 g/l
Granules according to the invention can be prepared by dispersing pyrogenic titanium dioxide in water and then spray-drying.
The invention also provides granules based on pyrogenic titanium dioxide with the following physico-chemical characteristics:
Average particle diameter: 10 to 160 xcexcm
BET surface area: 15 to 100 m2/g
pH: 3.0 to 9.0
Compacted density: 400 to 1,200 g/l
Carbon content: 0.3 to 12.0 wt. %
Granules according to the invention can be prepared by dispersing pyrogenic titanium dioxide in water, spray-drying and then silanizing the product. Halogenated silanes, alkoxysilanes, silazanes and/or siloxanes are used for silanizing.
The following substances may be used in particular as halogenated silanes:
Halogenated organosilanes of the type X3Si (CnH2n+1)
X=Cl, Br
n=1-20.
Halogenated organosilanes of the type X2(Rxe2x80x2)Si(CnH2n+1)
X=Cl, Br
Rxe2x80x2=alkyl
n=1-20.
Halogenated organosilanes of the type X(Rxe2x80x2)2Si(CnH2n+1)
X=Cl, Br
Rxe2x80x2=alkyl
n=1-20.
Halogenated organosilanes of the type X3Si(CH2)mxe2x80x94Rxe2x80x2
X=Cl, Br
m=0, 1-20
Rxe2x80x2=alkyl, aryl (e.g. xe2x80x94C6H5)
xe2x80x94C4F9, xe2x80x94OCF2xe2x80x94CHFxe2x80x94CF3, xe2x80x94C6F13, xe2x80x94Oxe2x80x94CF2xe2x80x94CHF2 
xe2x80x94NH2, xe2x80x94N3, xe2x80x94SCN, xe2x80x94CHxe2x95x90CH2,
xe2x80x94OOC(CH3)Cxe2x95x90CH2 
xe2x80x94OCH2xe2x80x94CH(O)CH2 
xe2x80x94NHxe2x80x94COxe2x80x94Nxe2x80x94COxe2x80x94(CH2)5 
xe2x80x94NHxe2x80x94COOxe2x80x94CH3, xe2x80x94NHxe2x80x94COOxe2x80x94CH2xe2x80x94CH3, xe2x80x94NHxe2x80x94(CH2)3Si(OR)3 
xe2x80x94Sxxe2x80x94(CH2)3Si(OR)3, where R is alkyl.
Halogenated organosilanes of the type (R)X2Si(CH2)mxe2x80x94Rxe2x80x2
X=Cl, Br
R=alkyl
m=0, 1-20
Rxe2x80x2=alkyl, aryl (e.g. xe2x80x94C6H5)
xe2x80x94C4F9, xe2x80x94OCF2xe2x80x94CHFxe2x80x94CF3, xe2x80x94C6F13, xe2x80x94Oxe2x80x94CF2xe2x80x94CHF2 
xe2x80x94NH2, xe2x80x94N3, xe2x80x94SCN, xe2x80x94CHxe2x95x90CH2,
xe2x80x94OOC(CH3)Cxe2x95x90CH2 
xe2x80x94OCH2xe2x80x94CH(O)CH2 
xe2x80x94NHxe2x80x94COxe2x80x94Nxe2x80x94COxe2x80x94(CH2)5 
xe2x80x94NHxe2x80x94COOxe2x80x94CH3, xe2x80x94NHxe2x80x94COOxe2x80x94CH2xe2x80x94CH3, xe2x80x94NHxe2x80x94(CH2)3Si(OR)3 
xe2x80x94Sxxe2x80x94(CH2)3Si(OR)3, where R is alkyl.
Halogenated organosilanes of the type (R)2XSi(CH2)mxe2x80x94Rxe2x80x2
X=Cl, Br
R=alkyl
m=0, 1-20
Rxe2x80x2=alkyl, aryl (e.g. xe2x80x94C6H5)
xe2x80x94C4F9, xe2x80x94OCF2xe2x80x94CHFxe2x80x94CF3, xe2x80x94C6F13, xe2x80x94Oxe2x80x94CF2xe2x80x94CHF2 
xe2x80x94NH2, xe2x80x94N3, xe2x80x94SCN, xe2x80x94CHxe2x95x90CH2,
xe2x80x94OOC(CH3)Cxe2x95x90CH2 
xe2x80x94OCH2xe2x80x94CH(O)CH2 
xe2x80x94NHxe2x80x94COxe2x80x94Nxe2x80x94COxe2x80x94(CH2)5 
xe2x80x94NHxe2x80x94COOxe2x80x94CH3, xe2x80x94NHxe2x80x94COOxe2x80x94CH2xe2x80x94CH3, xe2x80x94NHxe2x80x94(CH2)3Si(OR)3 
xe2x80x94Sxxe2x80x94(CH2)3Si(OR)3, where R is alkyl.
The following substances may be used in particular as alkoxysilanes:
Organosilanes of the type (RO)3Si(CnH2n+1)
R=alkyl
n=1-20
Organosilanes of the type Rxe2x80x2x(RO)ySi(CnH2n+1)
R=alkyl
R=alkyl
n=1-20
x+y=3
x=1, 2
y=1, 2
Organosilanes of the type (RO)3Si(CH2)mxe2x80x94R
R=alkyl
m=0, 1-20
Rxe2x80x2=alkyl, aryl (e.g. xe2x80x94C6H5)
xe2x80x94C4F9, xe2x80x94OCF2xe2x80x94CHFxe2x80x94CF3, xe2x80x94C6F13, xe2x80x94Oxe2x80x94CF2xe2x80x94CHF2 
xe2x80x94NH2, xe2x80x94N3, xe2x80x94SCN, xe2x80x94CHxe2x95x90CH2,
xe2x80x94OOC(CH3)Cxe2x95x90CH2 
xe2x80x94OCH2xe2x80x94CH(O)CH2 
xe2x80x94NHxe2x80x94COxe2x80x94Nxe2x80x94COxe2x80x94(CH2)5 
xe2x80x94NHxe2x80x94COOxe2x80x94CH3, xe2x80x94NHxe2x80x94COOxe2x80x94CH2xe2x80x94CH3, xe2x80x94NHxe2x80x94(CH2)3Si(OR)3 
xe2x80x94Sxxe2x80x94(CH2)3Si(OR)3 
Organosilanes of the type (Rxe2x80x3)x(RO)ySi(CH2)mxe2x80x94Rxe2x80x2
R=alkyl
m=0, 1-20
Rxe2x80x3=alkyl x+y=3
x=1, 2
y=1, 2
Rxe2x80x2=alkyl, aryl (e.g. xe2x80x94C6H5)
xe2x80x94C4F9, xe2x80x94OCF2xe2x80x94CHFxe2x80x94CF3, xe2x80x94C6F13, xe2x80x94Oxe2x80x94CF2xe2x80x94CHF2 
xe2x80x94NH2, xe2x80x94N3, xe2x80x94SCN, xe2x80x94CHxe2x95x90CH2,
xe2x80x94OOC(CH3)Cxe2x95x90CH2 
xe2x80x94OCH2xe2x80x94CH(O)CH2 
xe2x80x94NHxe2x80x94COxe2x80x94Nxe2x80x94COxe2x80x94(CH2)5 
xe2x80x94NHxe2x80x94COOxe2x80x94CH3, xe2x80x94NHxe2x80x94COOxe2x80x94CH2xe2x80x94CH3, xe2x80x94NHxe2x80x94(CH2)3Si(OR)3 
xe2x80x94Sxxe2x80x94(CH2)3Si(OR)3 
The silane Si 108 [(CH3O)3xe2x80x94Sixe2x80x94C8H17] trimethoxyoctylsilane is preferably used as a silanizing agent.
The following substances may be used in particular as silazanes:
Silazanes of the type 
R=alkyl
Rxe2x80x2alkyl, vinyl
and also, for example, hexamethyldisilazane.
The following substances may be used in particular as siloxanes:
Cyclic polysiloxanes of the types D 3, D 4, D 5, e.g. hexamethylcyclotrisiloxane=D 3
e.g. octamethylcyclotetrasiloxane=D 4
e.g. decamethylcyclopentasiloxane=D 5
Polysiloxanes or silicone oils of the type 
Y=CH3, H, CnH2n+1, n=1-20
y1=Si(CH3)3, Si(CH3)2H
Si(CH3)2OH, Si(CH3)2(OCH3)
Si(CH3)2(CnH2n+1), n=1-20
R=alkyl, aryl, (CH2)nxe2x80x94NH2, H
Rxe2x80x2=alkyl, aryl, (CH2)nxe2x80x94NH2, H
Rxe2x80x3=alkyl, aryl, (CH2)nxe2x80x94NH2, H
Rxe2x80x2xe2x80x3=alkyl, aryl, (CH2)nxe2x80x94NH2, H
The carbon content of granules according to the invention may be 0.3 to 12.0 wt. %.
The dispersion in water may have a titanium dioxide concentration of 3 to 25 wt. %.
Organic auxiliary substances may be added to the dispersion in order to increase the stability of the dispersion and to improve the particle morphology after spray-drying.
The following auxiliary substances may be used, for example:
polyalcohols, polyethers, surfactants based on fluorinated hydrocarbons, alcohols.
Spray-drying may be performed at a temperature of 200xc2x0 to 600xc2x0 C. Spinning disc atomizers or nozzle atomizers may be used.
Silanizing may be performed using the halogenated silanes, alkoxysilanes, silazanes and/or siloxanes described above, wherein the silanizing agent may optionally be dissolved in an organic solvent such as, for example, ethanol.
The silane Si 108 [(CH3O)3xe2x80x94Sixe2x80x94C8H17] trimethoxyoctylsilane may preferably be used as the silanizing agent.
Silanizing may be performed by spraying the granules with silanizing agent at room temperature and then thermally treating the mixture at a temperature of 105xc2x0 to 400xc2x0 C. for a period of 1 to 6 hours.
An alternative method of silanizing the granules may be performed by treating the granules with the silanizing agent in vapor form and then thermally treating the mixture at a temperature of 200xc2x0 to 800xc2x0 C. for a period of 0.5 to 6 hours.
Thermal treatment may be performed under a protective gas such as, for example, nitrogen.
Silanizing may be performed continuously or batchwise in heatable mixers and dryers with spray devices. Suitable devices may be, for example: plough bar mixers, disc dryers, fluidized bed dryers or moving bed dryers.
The physico-chemical parameters of the granules, such as the specific surface area, particle size distribution, compacted density and pH, may be modified within the limits given above by varying the substances used and the conditions used during spraying, heating at constant temperature and silanizing.
Titanium dioxide granules according to the invention have the following advantages:
The flow behavior is better than non-spray-dried titanium dioxide.
Incorporation into organic systems is easier. Dispersion is simpler.
No additional auxiliary substances are required for granulation.
Titanium dioxide granules according to the invention have a defined particle size, unlike non-spray-dried titanium dioxide which does not have a defined agglomerate size. Titanium dioxide granules according to the invention can be handled in a dust-free manner.
Lower packaging costs are required for transportation due to the high compacted density.
Titanium dioxide granules according to the invention can be used as a catalyst support.
Non-spray-dried titanium dioxide is not suitable for this purpose.
Granules according to the invention may be used as a support for catalysts, and also in cosmetics, as a sunscreen, in silicone rubber, in toning powder, in lacquers and colorants, as a grinding and polishing agent and as a raw material for producing glass and ceramics.